1. Field of the Invention
The present invention relates to computed tomographic imaging such as a nuclear magnetic resonance imaging and, more particularly, to computed tomographic imaging capable of a multi-slice imaging in which imagings are carried out at a plurality of slicing positions equidistantly apart.
2. Description of the Background Art
Conventionally, a nuclear magnetic resonance imaging apparatus typically has a configuration shown in FIG. 1, where it is shown to be comprised of a frame 1 containing an imaging system, and a bed 2 for carrying a patient 3. The bed 2 has a slidable top plate 4 over which the patient 3 is placed, and a lift 5 for adjusting the height of the top plate 4. The frame 1 has a bore 1A into which the top plate 4 is to be slid in, a first projector 6 for illuminating a side of the patient 3 at the opening of the bore 1A, a second projector 7 for illuminating a top of the patient 3 at the opening of the bore 1A, and a control panel 8 for manually controlling the sliding of the top plate 4 into the bore 1A.
The illuminations by the first and second projectors 6 and 7 are provided for the purpose of determining the position of a part of the patient 3 to be imaged. As shown in FIG. 2, the first projector 6 projects a cross-shaped beam 6B along an X axis. This X-directed beam can be inclined by an angle .theta.x causing the beam to move in a Y-direction across the side of the patient 3. The second projector 7 projects a cross-shaped beam 7B in a Y direction.
In taking a multi-slice image, the top plate 4 and the lift 5 are adjusted such that the center of the part of the patient 3 to be imaged meets with the centers of the cross-shaped beams 6B (X cross-shaped beam) and 7B (Y cross-shaped beam). The X cross-shaped beam 6B must be inclined in the Y-direction when the height of the top plate 4 is insufficient because of some structural limitation, or when desired slice image is transverse to the sagittal plane (Y-Z plane).
Then, as shown in FIG. 3, the slicing angle and the positions of the centers of the X and Y cross-shaped beams measured by potentiometers in the first projector 6 is transmitted to a control unit 10 so as to obtain a display on a display unit 11. The second projector 7 does not produce any signal since it has a fixed position. After the patient 3 has been carried into the bore 1A, the other parameters required for the single-slice imaging such as a type of slicing plane, i.e., a sagittal plane (Y-Z plane), a coronal plane (X-Z plane), or an axial plane (X-Y plane), as well as the multi-slice imaging conditions such a number of slices, a slice thickness, and an imaging time interval TR for receiving nuclear magnetic resonance signals will be entered manually from an operation unit 9.
Then, a quick single-slice imaging called a scanner image will be taken. This scanner image is taken along a plane which is perpendicular to the plane to be used for the multi-slice imaging. The precise positions of each of the multi-slices of the object image can be determined from this scanner image. For this reason, the imaging conditions for this scanner image are set such that it can be done in a short time (less than a few minutes), and sufficient image quality can be obtained for precisely determining the positions of the multi-slices. To accomplish this quick scanner image, picture elements are made to be coarser and multiplicity of data reading is reduced.
After the scanner imaging, the imaging conditions required for the multi-slice imaging such as a number of slices, a slice thickness, and an imaging time interval TR, as well as the imaging parameters required for the multi-slice imaging such as a view field, a coarseness of picture elements, a multiplicity of data reading, slice positions, and a slice angle are entered manually from the operation unit 9.
Here, when the number of slices is made larger and at the same time the imaging time interval TR is made longer, the nuclear magnetic resonance signals received weaken substantially, so that the image quality is severely damaged. Thus, once the imaging time interval TR is given the maximum number of slices can be automatically determined to achieve a satisfactory level of image quality, and vice versa. The number of slices and the slice thickness selected within this limitation will then determine the desired imaging region. For example, when the slice thickness is 10 mm and the number of slices is 10, the desired imaging region has a thickness of 100 mm.
However, since the scanner imaging is limited by the view field used, it has often been the case that an entire imaging region determined on a basis of the desired positions and angles of the multi-slice is too large to be imaged by the scanner in a single operation. In other words, proper fitting of the imaging region into the scanner image has conventionally depended on the experience and skill of an operator. In particular, since the relation and skill of an operator. In particular, since the relation between the imaging region and the imaging time interval TR has conventionally been obscure to the operator, such a proper fitting of the imaging region into the scanner image has been a difficult task, so that re-taking of the scanner image has often been necessary.
Furthermore, at the time of positioning the patient 3 it has not been possible to know the maximum number of slices which may be imaged.